The neurobiology of social attachment remains a relatively uninvestigated area that should prove relevant to psychiatry, psychology, and developmental psychobiology. Recent studies with a monogamous rodent, the prairie vole (Microtus ochrogaster), have provided a reliable behavioral index for quantitative studies of social attachment. Prairie voles exhibit a sustained partner preference (preference for a mate versus a conspecific stranger) after mating. Previous research has demonstrated the importance of this preference for pair bonding and the role of oxytocin in this process. In addition, consistent with dopamine's effects on reward and learning, we have recently demonstrated that a D2 receptor antagonist blocks mating-induced partner preferences whereas a D2 agonist facilitates preference formation in the absence of mating. In the present application, we propose four studies to systematically investigate the relationship between mating, dopamine, and social attachment. In a first study, we will identify the specific brain areas critical for dopamine regulation of partner preferences in prairie voles. We will also examine the role, if any, that regional dopamine plays in the regulation of social behavior in montane voles (M. montanus), a promiscuous species that does not form pair bonds after mating but resembles the prairie vole in many non-social behaviors. In a second study, we will compare the two species of voles in their regional dopaminergic markers. In a third study, we will investigate whether mating affects dopamine release differentially in the two species. Finally, we will study the interaction between dopamine and oxytocin in the regulation of partner preferences. Together, these studies should provide a comprehensive understanding of the role of dopaminergic pathways in the physiological process of social attachment. By adopting a comparative approach, these studies may not only reveal a proximate mechanism by which mating and dopamine facilitate social attachment but also suggest how a specific monoaminergic system has been adapted for quite different behavioral functions in closely related species.